Schizophrenia is a chronic, debilitating mental disorder characterized by positive symptoms (psychosis), negative symptoms (apathy) and cognitive impairments as well as physiologic abnormalities such as hypofontality, disrupted eye tracking and abnormal cortical event related potentials. The syndromic features can best be replicated in normal volunteers by the administration of subanaesthetic doses of dissociative anaesthetics, which are non-competitive inhibitors of the NMDA receptor. Based on post-mortem findings, we proposed 15 years ago that cortical NMDA receptor hypofunction was a core pathophysiologic feature of schizophrenia, accounting for the enduring and disabling negative and cognitive symptoms whereas psychosis was down-stream complication of this primary cortical pathology. During the last period of support, we have shown with a mouse genetic model for the reduced availability of the NMDA receptor co- agonist, D-serine, in schizophrenia that these mice exhibit reduced dendritic complexity and fewer dendritic spines, neuronal pathology most likely responsible for negative symptoms and cognitive impairments in schizophrenia. In the proposed studies, we will resolve a controversy over the cellular localization of serine racemase (SR), which synthesizes D-serine, by exploiting cell specific expression of Cre to inactivate SR in neurons or astrocytes. Using these mutants, we will determine how synaptic D-serine is regulated during glutamatergic neurotransmission. We will then determine how D-serine deficiency affects dendritic maturation and spine formation, when in development and what is the gene expression signature of this effect. This expression profile will be compared to that found in the cortex in schizophrenia and in other mouse mutants of schizophrenia. Finally, we will determine whether the dendritic dysplasia of the SR mutant mice is reversible by treatments that enhance NMDA receptor function. It is our hope that by further characterizing the consequences of impaired NMDA receptor function in schizophrenia new targets for pharmacotherapeutic intervention will be identified that will address the recalcitrant negative symptoms and cognitive impairments.